The present invention relates to a method for electrodepositing a protein onto an ion-exchange membrance by electrophoresis from a solution in which the protein has been dissolved or dispersed in suspension and an apparatus for the electrodepositing thereof.
The technique of depositing an electrically charged high molecular substance by electrophoresis on an electrode has been well known and hitherto been widely applied in industrial fields including the field of painting.
The advantage of this method of depositing resides in that the high molecular substance can be electrodeposited in a relatively uniform thickness on the electrodes of any shape, and that thermal steps such as evaporation are not necessary for separating the charged substance and the liquid in which the charged substance had been included.
On the other hand, however, since the electrically charged substance is directly deposited on the electrodes in the above-mentioned well known method, there are drawbacks such as the simultaneous occurrence of reactions between the charged high molecular substance and the electrodes, those between the high molecular substance and various gases generated by the simultaneously occurring electrolysis of water. Especially, in cases where the above-mentioned well known method is applied on the separation of bio-high molecular substances, since such substances are apt to be subjected to the effects of oxidation, reduction, etc., unfavorable phenomena of chemical changes such as degeneration, deterioration, etc. are frequently observed.
Moreover, in the case where the above-mentioned well known method is applied to the electrodepositing of bio-high molecular substances such as proteins, the following drawbacks are frequently noticed:
(1) In the case where a high molecular substance is electrically deposited on the surface of an electrode, gases such as oxygen and hydrogen are generated usually due to electrolysis of water on the surface of the electrode and these gases persist within the film of the electrodeposited high molecular substance on the surface of the electrode and as a result, it is frequently impossible to obtain a foamless film of the substance,
(2) It is necessary to give an appropriate electric charge to the high molecular substance in order to move the substance toward the surface of the electrode by electrophoresis, and as a condition for such a step, the pH of the high molecular substance is especially important.
However, there are many cases where such a condition is not necessarily most appropriate for electrically depositing the high molecular substance to the surface of the electrodes. In other words, the overvoltage of the electrode usually fluctuates widely due to the conditions by which an appropriate charge is given to the high molecular substance such as pH, and for that reason, there are many cases where a high operational voltage is necessary or, in certain circumstances, the electrode is affected,
(3) Even in cases where the conditions of electrophoresis of the high molecular substance to the surface of the electrode are fulfilled, since on the electrodepositing of the high molecular substance, for instance, a water-soluble protein, the protein is deposited on the surface of the electrode in a state of still containing water absorbed by the protein, it is frequently impossible to obtain an electrodeposited layer of protein in a high density accompanied by an appropriate dehydration. This phenomenon is due to the facts that the conditions for electrophoresis and the conditions for dehydration of the protein are different, and especially, that the dependencies of both conditions on pH is different from each other. In addition, in the process of usual methods of the electrodepositing, it is extremely difficult to adjust both the two conditions, and
(4) According to the construction of the electrode used for electrodepositing, there are cases where the charged high molecular substance, for instance, a protein, and the surface of the electrode get tangled together in the progress of the formation of the electrodeposited layer of the high molecular substance, or the layer comes to hold the gases generated. As a result, the operating voltage is raised drastically as time passes not only to reduce the recovery of the protein but also to make the removal of the protein layer from the electrode difficult and to impair the quality of the deposited film layer of protein remarkably.
Accordingly, the object of the present invention is to offer a method of effectively producing a homogeneous film of protein not containing any bubbles by a process of electrodepositing in the utilization of electrophoresis from a liquid in which the protein is dissolved or dispersed in suspension.
Another object of the present invention is to offer a method according to the above-mentioned process of electrodepositing for effectively recovering the protein.
Still another object of the present invention is to offer an apparatus for carrying out the above-mentioned methods.
The inventors have found that in the case where a protein is electrically deposited, utilizing electrophoresis, from a liquid in which the protein is dissolved or dispersed in suspension, the above-mentioned object is satisfied by interposing an ion-exchange membrane between the above-mentioned liquid and the electrode and by causing the protein not to be deposited onto the surface of the electrode but onto the ion-exchange membrane.
The following is the explanation of the present invention in detail: